Solution for plating metals with gold



Patented Mar. 28, 1950 SOLUTION FOR PLATING METALS WIT-H GOLD Ralph W.Porter, J12, Cambridge, and Clifford M. Jones, Chelsea, Mass.

No Drawing. Application September 11, 1946, Serial No. 696,380

3 Claims.

This invention relates to the plating of metals by mere immersionwithout heat or electrolytic action, and more especially to the platingof base metals with gold in this manner.

Heretofore, metals have been plated with gold by electrolysis, a methodwhich requires the heating of the solution. The heating of the solutioncauses evaporation, which results in reducing the plating efiiciencythereof. An electrolytic solution is weakened, also, by thetransposition of gold from "the gold anode thereof to the solutionbecause the gold transposed from the anode to the solution does notenter into composition with the gold chloride solution.

Our method, in addition to being more economical than the electrolyticmethod, produces a more even coating of gold, which eliminates thenecessity for vbufiing. No gold anode is required and the platingprocess is carried out with a cold solution.

One of the uses to which our invention may be put is the plating ofgrids of radio tubes and other electron discharge devices. It has longbeen the practice to plate the grids of radio tubes electrolytically toreduce the absorption of air by the grid and diminish the secondaryemission therefrom due to molecular bombardment. It has been theexperience of tube makers that when tubes having gold-plated grids arebombed, the gold particles fiy on" the grids, which usually are made ofmolybdenum or tungsten and are supported by nickel .side rods. However,when the grids are plated by our composition andprocess, the platingwill remain intact under the bombing process.

Our process and solution may also be used in plating the interiorsurface of a hypodermic needle, which is about two-hundredths of an inchin diameter, without clogging, thereby prolonging the useful life of theneedle, the inner surfaces of which frequently corrode and causeclogging.

We have found that various metals, for example, nickel, tungsten, andmolybdenum, can be plated with gold by mere immersion in our solutionand without the use of electrolysis or heat.

The solution which we prefer at the present time comprises distilledwater, gold chloride, so-

dium phosphate, potassium cyanide, and acetic acid, and, when the metalto be plated is nickel, nickel chloride (nickel carbonate) is included.

The quantities of the ingredients of our solution having a water contentof 375 cubic centimeters (375 grams) of distilled water, which we havefound to be the minimum practicable solution, are substantially asfollows, prior to dissolving them in 375 cubic centimeters of distilledwater:

Gold chloride 3.9 grams; nickel chloride or carbonate, when used, 3.9grams; sodium phosphate, tribasic, 47.5 grams; potassium cyanide 47.5grams; acetic acid, 18 cubic centimeters, i. e., 18.88 grams.

Expressed in percentages, the quantitative relation of the ingredientsprior to dissolution in 375 cubic centimeters of distilled water, may bedefined substantially as follows:

Gold chloride .79% by weight; nickel chloride (carbonate), when used,79% by weight; sodium phosphate, tribasic, 9.57% by weight; potassiumcyanide 9.57% by weight; acetic acid 3.78% by weight (18 cubiccentimeters); distilled water 75.50% by weight.

When the metal to be plated is other than nickel, and the water contentof the solution is 375 cubic centimeters, (375 grams), the quantities ofthe ingredients prior to their dissolution in 375 cubic centimeters ofdistilled water are substantially as follows:

Gold chloride 3.9 grams; sodium phosphate 47.5 grams; potassium cyanide47.5 grams; acetic acid 18.0 cubic centimeters, i. e., 18.88 grams.

Expressed in percentages, the quantitative relation of the ingredientswhen nickel chloride (or nickel carbonate) is omitted, prior todissolution in 375 cubic centimeters of distilled water, may be definedsubstantially as follows:

Gold chloride 79% by weight; sodium phosphate 9.63% by weight; potassiumcyanide 9.63% by weight; acetic acid 3.82% by weight (18 cubiccentimeters); distilled water 76.13% by weight.

Our experience has been that the maximum practicable solution is onehaving a water content of about 4500 cubic centimeters.

It is to be understood that while we have stated specifically the exactquantities which we have found to be useful, practicable, and efficient,we do not limit ourselves thereto, because the proportions are capableof variations. We have found that the rate of increase of eachingredient with respect to the water content is substantially linear.

The ingredients preferably are mixed as follows, to wit: first, the goldchloride is completely dissolved in the distilled water; next, thesodium phosphate (tribasic) is added and thoroughly dissolved; then, thepotassium cyanide is dissolved therein; and finally, the acetic acid isadded to the solution, slowly and without agitation or stirring. Afterthe evolution of a negligible quantity of gas caused by the addition ofthe acetic acid has ceased, it is advisable to stir the solution toeffect the thorough dissolution of the ingredients and to insureuniformity throughout. The acetic acid co-ordinates the otheringredients into a solution that will give the desired result.

When the metal to be plated is nickel, the above procedure is followeddown to and including the addition to the solution of potassium cyanide,then the nickel chloride (or nickel carbonate) is added and thoroughlydissolved, and, finally, as before, the acetic acid is added in themanner above set forth. When nickel chloride is used, the solution mustbe stirred to effect the thorough dissolution of the same, but whennickel carbonate is used, there will be a violent evolution of gas whichwill effect the thorough dissolution of the nickel carbonate.understood, of course, that nickel carbonate is the full chemicalequivalent of nickel chloride, insofar as the present invention isconcerned. The nickel salt is necessary only when the metal to be platedwith gold is nickel. By the solution containing nickel chloride(carbonate) metals other than nickel can be plated with gold, e. g.,tungsten and molybdenum, which frequently are used for the side bars orsupports of radio tubes and other electron discharge devices.

The grid wire, or other metallic member to be plated, is placed in thesolution above described, and after remaining therein a short period oftime, for example, 15 seconds for a small grid, to about two minutes fora larger article, is removed by nonmetallic means, for example, glasspliers.

The solution is stable and will not deteriorate with lapse of time ifenclosed within asealed container.

We are aware that various solutions have been proposed for gildingmetals with gold. Our solution, however, is not to be confused with suchgilding solutions because the film of gold formed by them on othermetals is readily removed by scouring or even by handling, while by oursolution the metals immersed therein are plated with gold even morefirmly than by electrolytic deposition, as shown by the fact that whengrids of radio tubes are plated by our solution, the plating remainsprocess.

As at present advised, it is our belief that the acetic acid whendissolved in water breaks up into hydrogen ions or cations, which carryposi- It is to be intact under the bombing tive charges, and anions,which are ions carrying negative charges.

Acetic acid belongs to the class of so-called weak acids because only asmall portion of a given quantity thereof breaks up into hydrogen ionsor cations, and anions, upon the complete dissolution of such quantityin water. It is for this reason, as we believe, that acetic acid is thebest acid for use as the acid element of our solution.

Having thus described illustrative embodiments of our invention,without, however, limiting the same thereto, what we claim and desire tosecure by Letters Patent is:

1. A solution for plating metals with gold by immersion only, comprisingbefore the dissolution thereof in distilled water, the followingingredients in substantially the proportions by weight hereinafterstated, to wit, gold chloride .79 nickel chloride .79%, tribasic sodiumphosphate 9.57%, potassium cyanide 9.57%, acetic acid 3.78%, anddistilled water 75.50%.

2. A solution for plating metals with gold by immersion only, comprisingbefore the dissolution thereof in distilled water, the followingingredients in substantially the proportions by weight hereinafterstated, to wit, gold chloride .79%, nickel carbonate .79%, tribasicsodium phosphate 9.57%, potassium cyanide 9.57 acetic acid 3.78%, anddistilled water 75.50%.

3. A solution for plating metals with gold by immersion only, comprisingbefore the dissolution thereof in distilled water, the followingingredients in substantially the proportions by weight hereinafterstated, to wit, gold chloride .79%, tribasic sodium phosphate 9.63%,potassium cyanide 9.63%, acetic acid 3.82%, and distilled water 76.13%.

RALPH W. PORTER, JR. CLIFFORD M. JONES.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the Number Name Date 744,170Darlay Nov. 17, 1903 1,208,507 Dalby Dec. 12, 1916 OTHER REFERENCES

3. A SOLUTION FOR PLATING METALS WITH GOLD BY IMMERSION ONLY, COMPRISINGBEFORE THE DISSOLUTION THEREOF IN DISTILLED WATER, THE FOLLOWINGINGREDIENTS IN SUBSTANTIALLY THE PROPORTIONS BY WEIGHT HEREINAFTERSTATED, TO WIT, GOLD CHLORIDE .79%, TRIBASIC SODIUM PHOSPHATE 9.63%,POTASSIUM CYANIDE 9.63%, ACETIC ACID 3.82%, AND DISTILLED WATER 76.13%.